Gallium nitride (GaN)-based semiconductor devices are generally known for having high breakdown voltage, high switching speed and low on-resistance characteristics. For example, GaN-based lateral heterojunction (e.g. AlGaN/GaN) devices have shown promise as the core power switching devices in high-performance power conversion systems.
While discrete GaN power devices have already shown better performance than conventional silicon power devices, the peripheral control/driving modules are mainly implemented with a separate silicon-based integrated circuit (IC), leading to a Si-driver/GaN-switch hybrid driving solution. With such a hybrid solution, the inter-chip bonding wires or interconnects on a printed circuit board would present significant parasitic inductances/capacitances, which tend to degrade the circuit performance under high-frequency switching operations.
A two-stage gate driver integrated with a GaN power device has been realized previously. However, the circuit topology of this device has a number of adverse issues, including that the source current drops quickly with increased output voltage, as a result of the reduced gate-to-source voltage of one of the enhancement-mode transistors in the buffer stage when the load is being charged up; the charging process severely slows down when the source current becomes very small as the gate-to-source voltage approaches the device's threshold voltage. Another issue with this circuit is that the amplitude of the output voltage is smaller than the supply voltage, raising the possibility that power devices driven with this circuit cannot be fully turned on. The problem is even more severe when the gate driver is integrated with a power device with a larger threshold voltage. Using a larger supply voltage in the gate driver circuit may alleviate this problem, but would result in a larger gate voltage stress on some of the gate driver's inverter transistors and the corresponding larger power consumption in the driver circuit.